1. Field of the Invention
The present invention relates to a positive resist composition suitably used in the microlithography process at the production of VLSI or high-capacity microchip or in other photo-fabrication processes. More specifically, the present invention relates to a positive resist composition capable of forming a highly refined pattern by using vacuum ultraviolet light of 160 nm or less.
2. Description of the Related Art
The integration degree of integrated circuits is more and more increasing and in the production of a semiconductor substrate of VLSI or the like, an ultrafine pattern comprising lines having a width of quarter-micron or less must be processed. One known method for attaining the refinement of pattern is to use an exposure light source having a short wavelength at the formation of a resist pattern.
For example, in the production of a semiconductor device having an integration degree up to 64 M bits, the i-line (365 nm) of a high-pressure mercury lamp has been used as a light source until today. As the positive resist capable of responding to this light source, a large number of compositions containing a novolak resin and a naphtho-quinonediazide compound as a photosensitive material have been developed and these are sufficiently effective in the processing of lines in a width up to about 0.3 μm. Also, in the production of a semiconductor device having an integration degree of 256 M bits or more, a KrF excimer laser (248 nm) has been used as a light source in place of the i-line.
Furthermore, for the purpose of producing a semiconductor having an integration degree of 1 G bits or more, studies are being recently made on use of a light source having a further shorter wavelength, that is, an ArF excimer laser (193 nm) or in order to form a pattern of 0.1 μm or less, an F2 excimer laser (157 nm).
To cope with this tendency to shorter wavelength of the light source, the constituent components of the resist material and the compound structure thereof are also greatly changing.
As a resist composition for exposure by a KrF excimer laser, there has been developed a so-called chemical amplification-type resist composition where a resin having a basic skeleton of poly(hydroxystyrene) which shows small absorption in the region of 248 nm, and protected with an acid decomposable group is used as the main component and this is combined with a compound capable of generating an acid upon irradiation with far ultraviolet ray.
Also, as the resist composition for exposure by an ArF excimer laser (193 nm), there has been developed a chemical amplification-type resist using an acid-decomposable resin where an alicyclic structure having no absorption at 193 nm is introduced into the main or side chain of the polymer.
However, for the F2 excimer laser ray (157 nm), this alicyclic resin is found to show large absorption in the region of 157 nm and be insufficient for obtaining the objective pattern of 0.1 μm or less. On the other hand, a resin having introduced thereinto a fluorine atom (perfluoro structure) has been reported to have sufficiently high transparency to light at 157 nm in Proc. SPIE., Vol. 3678, page 13 (1999) and effective fluororesin structures have been proposed, for example, in Proc. SPIE., Vol. 3999, page 330 (2000), Proc. SPIE., Vol. 3999, page 357 (2000), Proc. SPIE., Vol. 3999, page 365 (2000) and International Publication WO-00/17712, pamphlet. Thus, studies on the resist composition using a fluorine-containing resin are being made.
However, the fluororesin-containing resist composition for exposure with F2 excimer laser light has a problem in the sensitivity or in that at the formation of a line-and-space pattern, the top end of line is rounded (round top) or a large amount of development residue (scum) remains in the bottom of space. Improvements of these points are demanded.